There is one thing that everyone needs to know about the 7mm RUM. It is .004 thousandths
longer in the body and .018 longer at the neck shoulder junction.

So It requires sizing down (Bumping the shoulder) .004 thousandths before it will chamber in
the 300 RUM.

300 Rum Brass is scarce and 7mm RUM is also but it can/will be available some day.

The only other option is to buy the managed recoil ammo from Remington for $35 to $40.00
and shoot it for break in or fouling shots and end up with fire formed brass in your chamber for
very little more than the price of brass.

J E CUSTOM

If the 7rum is slightly longer in the body and neck then why wasn't it the case of choice for the 338edge? Or is the different insignificant?